JP4385825B2 - Proximity sensor - Google Patents

Description

  The present invention relates to a proximity sensor that is used for the purpose of determining the presence or absence of a metal object or measuring the distance to a metal object by using a change in oscillation amplitude of an oscillation circuit including a coil.

  As this type of proximity sensor, there is one in which a range (detection distance) in which a metal object to be detected (hereinafter simply referred to as “object”) can be detected can be variably set in accordance with a user's adjustment operation. As a typical example, a variable resistor is incorporated in the oscillation circuit, and the current flowing in the feedback circuit of the oscillation circuit is changed by a rotation operation on the variable resistor.

  In the following Patent Document 1, a proximity sensor having the above-described configuration is introduced as a conventional example, and then a sensor of an improved configuration is proposed. This improved type of sensor incorporates a sensitivity adjustment circuit that includes multiple series of resistors and switches. By switching the combination of resistors used for sensitivity adjustment under the control of a microcomputer, the feedback current to the resonance circuit The amount is controlled (see FIG. 1 of Patent Document 1). In addition, Patent Document 1 discloses a proximity sensor having a configuration in which the amount of feedback current is adjusted by switching the resistance of a current mirror circuit that determines the feedback current (see FIG. 15 of Patent Document 1). ).

Japanese Patent No. 3440566

  When adjusting the magnitude of the feedback current using a variable resistor, the relationship between the amount of rotation of the variable resistor and the detection distance is nonlinear, making it difficult to grasp the amount of operation necessary to obtain the desired detection distance. is there. For this reason, it is necessary for the operator to repeat the adjustment operation and the operation check of the sensor by the adjustment, and there is a problem that the adjustment takes time.

  In addition, proximity sensors of the type that the user performs adjustment operations rely on the operator's intuition and experience to determine whether adjustment is appropriate, and determine whether the adjusted oscillation amplitude has the appropriate sensitivity for detecting objects. No indication is given to do this.

  When a plurality of proximity sensors having the same performance are arranged and the same detection distance is set for each sensor, it is desirable to make the sensitivity of each sensor uniform. However, conventional sensors that perform adjustment using variable resistance are not devised to accurately grasp the amount of operation, and even a slight shake of the hand may cause variations in adjustment. It is difficult to make uniform adjustments to the sensor. Even if one expert makes adjustments to each sensor, it is difficult to avoid variations in sensitivity for each sensor for the same reason.

  On the other hand, according to the proximity sensor disclosed in Patent Document 1, a combination of resistors is determined by the control of the microcomputer. Therefore, if a large number of resistors are provided, appropriate sensitivity adjustment is performed according to the detection distance to be set. It can be carried out. However, when a large number of resistors are provided, the number of parts increases, and there is a problem in that the size of the airframe increases and the cost increases. This proximity sensor is also not provided with means for notifying the user how the sensitivity has been set.

The present invention has been made paying attention to the above problem, and by adjusting the magnitude of the voltage applied to the feedback circuit of the oscillation circuit by digital control, the sensitivity can be finely adjusted with a small number of parts. Is the first purpose.
In addition, the present invention improves the sensitivity adjustment accuracy by adjusting the sensitivity according to the operator's adjustment operation, by indicating an index for eliminating the variation in the sensitivity to be set or setting the optimum sensitivity. The second purpose is to increase.

  A proximity sensor according to the present invention includes an oscillation circuit including a coil, detection means for detecting a metal object using the oscillation amplitude of the oscillation circuit, output means for outputting a detection result by the detection means, the coil and the metal Adjusting means for adjusting the state of change of the oscillation amplitude with respect to the change of the distance to the object.

  The detection means of the proximity sensor can include a determination means for determining the presence or absence of an object by comparing the oscillation amplitude with a predetermined threshold value. Further, it is possible to include a measuring means for measuring the distance from the coil to the object by checking the oscillation amplitude value against a predetermined table. These discriminating means and measuring means can be configured as a logical operation circuit including a comparator or the like, but are preferably configured by a computer in which a program corresponding to the function of the means is set.

  The output means can be configured as a circuit that outputs a detection result (the presence or absence of an object, a distance to the object, etc.) by the detection means to the outside as a digital or analog signal. Further, the adjusting means adjusts the magnitude of the change in the oscillation amplitude with respect to the change in the distance between the coil and the metal object, or changes the magnitude of the distance when the oscillation amplitude reaches a predetermined threshold value. Adjustments can be made.

  In the first proximity sensor according to the present invention, the oscillation circuit incorporates a feedback circuit designed so that the amount of feedback current varies depending on the applied voltage, and the adjusting means includes the oscillation circuit in the oscillation circuit. A signal generation unit that generates an adjustment signal indicating the level of a voltage applied to the feedback circuit as a digital quantity, and a signal output unit that analog-converts the adjustment signal and outputs the converted signal to the feedback circuit.

  Of the adjusting means, the signal generating means is preferably constituted by a computer in the same manner as the discriminating means and measuring means, but can also be constituted by a logic operation circuit. The signal output means can be constituted by a D / A converter for analog conversion of the adjustment signal generated by the signal generation means. Further, the signal output means may include a buffer, a voltage shift circuit, and the like.

  According to the proximity sensor configured as described above, the voltage level applied to the feedback circuit of the oscillation circuit is set as a digital amount adjustment signal, and then the voltage signal obtained by analog conversion of this adjustment signal is output to the feedback circuit. The voltage level can be controlled for each fixed unit corresponding to the resolution of the D / A conversion. Therefore, even if many circuits are not provided in parallel as in Patent Document 1, the current can be adjusted in fine units, and the sensitivity can be finely adjusted.

  In a preferred aspect of the proximity sensor, an operation unit for sensitivity adjustment and a display unit for displaying information indicating the value of the adjustment signal or information indicating the magnitude of the oscillation amplitude are provided. The signal generation means of the adjustment means sets the value of the adjustment signal according to the operation of the operation unit. Further, the proximity sensor uses the value of the adjustment signal set by the signal generation unit or the oscillation amplitude when the signal after the analog conversion of the adjustment signal is output to the feedback circuit. Display control means for controlling the display is provided.

  Said operation part and display part can be provided in the body (amplifier part in the case of the sensor which comprises the detection part containing a coil etc. and an amplifier part) which comprises a sensor main body. The operation unit may be a push button type switch or a numeric input key, but is not limited thereto, and may be configured by a lever or a volume. In addition, the operation unit may be configured to input the value of the adjustment signal itself, but is not limited thereto, and may input information that indirectly indicates the value of the adjustment signal. For example, the adjustment signal can be divided into a plurality of levels and an operation for selecting one of them can be performed.

  The display unit may be a numerical display that displays the adjustment signal and the oscillation amplitude value itself. Alternatively, a graph such as a bar graph or a pie graph or a symbol indicating a numerical level can be displayed. In the case of displaying a graph, a reading memory may be attached to the graph so that the numerical value can be read with high accuracy.

  The signal generation means can set the value of the adjustment signal in accordance with the number of times the push button switch is operated, the amount of rotation of the volume, and the like, and can provide this to the signal output means. The display control means generates display information suitable for the specifications of the display section using the value of the adjustment signal or the value of the oscillation amplitude measured immediately after the value is given to the signal output means. Can be output. This display control means is also preferably configured by a computer.

  According to the above configuration, when the operator performs an operation for adjusting the sensitivity, the applied voltage to the feedback circuit changes according to the operation, and the oscillation amplitude is adjusted. Here, if the value of the adjustment signal or the value of the oscillation amplitude suitable for adjustment is shown to the operator in advance, by performing the adjustment operation so that information indicating the presented value is displayed on the display unit, Appropriate sensitivity can be set. Even when the same detection distance is set for a plurality of proximity sensors having the same performance, the sensitivity between the sensors can be set uniformly by performing an adjustment operation based on the display on the display unit. Note that both the information indicating the value of the adjustment signal and the information indicating the magnitude of the oscillation amplitude can be displayed in parallel on the display unit. Moreover, both can be switched and displayed.

  Next, in another preferred aspect of the first proximity sensor, the adjustment unit is configured to change the value of the adjustment signal stepwise in a certain unit with respect to the signal generation unit. Control means for repeatedly executing until a predetermined value is reached, and registration means for registering the value of the adjustment signal when the oscillation amplitude reaches the predetermined value are provided.

  In the above, the “predetermined value” of the oscillation amplitude can be set in accordance with a threshold set in advance for determining the presence or absence of an object, or the oscillation amplitude when the oscillation is saturated. . This setting can be performed according to the characteristics of the oscillation circuit used and the application of the sensor.

  For example, when detecting the presence or absence of an object using a hard oscillation type oscillation circuit in which the range in which the oscillation amplitude changes is limited, a value that falls below the threshold with a sufficient margin is set as a predetermined value. be able to. In addition, when measuring the distance of an object within the detection distance range using an oscillation circuit having a characteristic in which the oscillation amplitude changes gradually, a value lower than the saturation level is set as the predetermined value. Can do. Furthermore, the predetermined value in this case is such that, regardless of the detection distance, a sufficient amplitude change occurs while the object moves in a predetermined range centered on the position corresponding to the detection distance. In this case, it is desirable to set the oscillation amplitude level (a level obtained at a position corresponding to the detection distance).

In the above aspect, the registration means can include a memory for storing the adjustment value to be registered.
According to this aspect, when the operator places the object to be detected at a desired position, the oscillation amplitude can be measured while automatically changing the value of the feedback current by the repetitive operation of the signal generating means. When the oscillation amplitude measured here is in a state where an object can be detected with high accuracy, the value of the adjustment signal at that time can be registered as an appropriate value. Thereafter, the amount of feedback current can be adjusted by the registered adjustment signal, so that the presence / absence determination of the object and the distance measurement can be performed with high accuracy.

  Further, the first proximity sensor is provided with a temperature measuring means (such as a temperature sensor) for measuring the ambient temperature, and the signal generating means of the adjusting means is provided with the adjustment based on the measured value by the temperature measuring means. Correction means for correcting the value of the signal can be included. According to this configuration, even if the ambient temperature fluctuates after an appropriate sensitivity is set, the value of the adjustment signal can be corrected according to the fluctuation, so that a proximity sensor that is resistant to temperature changes can be provided. it can.

  In the second proximity sensor according to the present invention, a feedback circuit designed so that the amount of feedback current varies depending on the applied voltage is incorporated in the oscillation circuit, and the value of the voltage applied to the feedback circuit is set. An operation unit for displaying the information, and a display unit for displaying information indicating the set value of the voltage or information indicating the oscillation amplitude. The adjusting means is set so as to apply a voltage according to the setting of the operation unit to a feedback circuit in the oscillation circuit.

In the above, the operation unit and the display unit can be configured in the same manner as described for the first proximity sensor.
The adjustment unit may include a signal generation unit and a signal output unit similar to those of the first proximity sensor. However, the adjusting means related to the second proximity sensor is not limited to digital control, but a mode in which the applied voltage is controlled by adjusting the value of the resistance applied to the feedback circuit (a mode in which the above-described variable resistance is incorporated or a plurality of modes). A mode of switching the resistance of the above can be included.

  According to the second proximity sensor, when the operator performs a voltage value setting operation, information indicating the set value of the voltage or the magnitude of the oscillation amplitude is displayed. Accordingly, by performing the setting operation until predetermined information is displayed on the display unit, it is possible to set an appropriate sensitivity according to the detection distance. In addition, it is possible to eliminate variations in sensitivity between sensors when the same detection distance is set for sensors having the same performance, and to improve measurement accuracy.

  In the second proximity sensor, a numerical display unit that displays a voltage set by the operation unit or a numerical value corresponding to the oscillation amplitude of the oscillation circuit to which the voltage is applied can be used as the display unit. In addition, when displaying a numerical value corresponding to the applied voltage, the displayed numerical value is not limited to the value of the applied voltage itself, but the voltage value after performing a correction such as adding an offset value or multiplying by a predetermined coefficient. It can also be displayed. It is also possible to display a reciprocal of the voltage value or a value uniquely obtained by substituting the voltage value into a predetermined arithmetic expression. However, this second proximity sensor can also perform analog display using graphs, bar codes, or the like instead of numerical values.

  Furthermore, in the proximity sensor according to the present invention, the adjusting means can be provided with voltage control means for controlling the voltage applied to the feedback circuit after the voltage is set by the operation unit. In this voltage control means, the applied voltage changes from a voltage for setting an oscillation amplitude of a magnitude that does not react to the metal object in response to an external signal, to a voltage that is higher than a voltage that should normally be set, The applied voltage is adjusted so that the voltage to be set normally is reached after a lapse of a predetermined time from the change.

  The above aspect can be applied to a case where each sensor is intermittently operated in order to prevent mutual interference between the sensors in a state where a plurality of proximity sensors are arranged in the vicinity. An external signal can be input from an external device that controls the intermittent operation. Further, intermittent operation can be controlled by performing communication between the plurality of proximity sensors without using an external device. In this case, transmission signals from other sensors can be considered as signals from the outside. For example, in each sensor, when the state that oscillates with a size capable of reacting to a metal object is considered as an `` operating state '', it is switched from a non-operating state to an operating state or from an operating state to a non-operating state. Sometimes, a signal indicating the switching can be transmitted to another sensor.

  Regardless of the type of external signal, the feedback circuit of each proximity sensor has an oscillation amplitude that is not large enough to react to a metal object when the other sensors are in operation (the amplitude is close to zero). It is desirable that a voltage is applied such that no voltage is applied, or no voltage is applied. When the operation becomes possible due to a change in the external signal, the applied voltage changes to a voltage larger than the voltage set during the previous sensitivity adjustment. Further, this voltage changes to the voltage set during the sensitivity adjustment when a predetermined time has elapsed.

  According to the above aspect, since a large voltage is temporarily applied to the feedback circuit immediately after switching from the non-operating state to the operating state, the oscillation amplitude can be increased immediately after the input of the signal. The time required for the oscillation amplitude to stabilize can also be shortened. Therefore, it is possible to provide a proximity sensor that has a high response speed and is resistant to noise at the time of startup.

  According to the present invention, the magnitude of the voltage applied to the feedback circuit of the oscillation circuit is adjusted by digital control, and the oscillation state is controlled by feeding back the current according to the magnitude of the applied voltage in the feedback circuit. As a result, the number of components can be reduced and the feedback current can be finely adjusted. Therefore, the sensitivity can be finely adjusted according to the characteristics of the oscillation circuit and the detection distance.

  Further, according to the present invention, when the sensitivity is adjusted according to the operator's operation, the adjustment is performed while checking the magnitude of the voltage applied to the feedback circuit by the operation or the magnitude of the oscillation amplitude adjusted by the voltage. Since the operation can be performed, it is possible to easily adjust the sensitivity to an appropriate level. In addition, even when setting the same detection distance to sensors with the same performance, it is possible to eliminate variations in sensitivity among sensors by performing work while checking the displayed content, and to perform highly accurate measurements. It becomes possible.

  FIG. 1 shows the appearance of a proximity sensor according to one embodiment of the present invention. The proximity sensor of this embodiment is configured by connecting a head unit 1, a preamplifier unit 3, and an amplifier unit 2 including a CPU via shielded cables 4 and 5, respectively. The head unit 1 and the preamplifier unit 3 function as a detection unit of the proximity sensor, and correspond to a distance from a detection surface (front surface) of the head unit 1 to a metal object to be detected (hereinafter referred to as “object”). A detection signal (representing the oscillation amplitude) is output. The amplifier unit 2 determines the presence or absence of an object using this detection signal, and outputs the determination result to the outside.

  An operation unit 22 including a plurality of switches and a display unit 21 are provided on the upper surface of the amplifier unit 2 of this embodiment, and the upper part thereof is protected by a lid unit 200. FIG. 2 shows a detailed configuration of the upper surface when the lid 200 is removed. In the figure, a display unit 21 is provided on the left hand, and an operation unit 22 is provided on the right hand.

  The display unit 21 includes an LED lamp 211 (hereinafter simply referred to as “lamp 211”) and four LED displays 212, and two sets of these combinations are arranged (hereinafter referred to as one set). (The combination of the eye lamp 211 and the LED display 212 is referred to as “display unit 21a”, and the combination of the second set of lamp 211 and the LED display 212 is referred to as “display unit 21b”.) The first set of display units 21a is configured by red LEDs, and the second set of display units 21b is configured by green LEDs.

  The operation unit 22 is provided with two selection keys 221, 222, a confirmation key 223, changeover switches 224, 225, and the like. The selection keys 221 and 222 and the confirmation key 223 are used in the setting mode. The changeover switch 224 is for switching between the setting mode and the normal operation mode, and the other changeover switch 225 is an operation of the output circuit 27 (on / off from the output circuit 27) to be described later at the time of object detection. Signal). In the setting mode, a character string indicating a setting item or a numerical value indicating a setting value is displayed on the display unit 21, and the display is switched according to the operation of the selection keys 221 and 222, and the confirmation key 223 is operated. The selection of items and set values are determined accordingly.

  The setting mode includes adjustment of sensitivity so that the user can detect an object at a desired position. This adjustment is performed by inputting an adjustment value of a predetermined magnitude from the operation unit 22 and controlling the feedback current of the oscillation circuit based on the adjustment value. Hereinafter, this adjustment value is referred to as “sensitivity adjustment value”.

  In this embodiment, after the initial value of the sensitivity adjustment value is displayed on one of the display units 21 (for example, the display unit 21a), the displayed numerical value is changed according to the operation of the selection keys 221 and 222, and the final value is displayed. Thus, the value displayed when the confirm key 223 is operated is confirmed as the sensitivity adjustment value. Note that the initial value of the sensitivity adjustment value is 0, and 1 is subtracted by the operation of the selection key 221 (however, it is not a negative value), and 1 is added by the operation of the selection key 222.

FIG. 3 shows a circuit configuration example of the proximity sensor.
This proximity sensor incorporates an oscillation circuit 10 for detecting a metal object. The oscillation circuit 10 includes a signal detection circuit 12, a feedback circuit 13, and the like, in addition to a resonance circuit 11 including a coil L and a capacitor C. Of these, the resonance circuit 11 is provided in the head unit 1, and the signal detection circuit 12 and the feedback circuit 13 are provided in the preamplifier unit 23. Note that the CPU 20 includes a memory storing a program and the like.

  On the other hand, in addition to the CPU 20 described above, the amplifier unit 2 incorporates a detection circuit 23, an A / D converter 24, a D / A converter 25, a voltage adjustment circuit 26, an output circuit 27, a power supply circuit 28, and the like. Further, the display unit 21 and the operation unit 22 described above are connected to the CPU 20.

  The detection circuit 23 and the A / D converter 24 are provided in the input path from the oscillation circuit 10 to the CPU 20. A D / A converter 25 and a voltage adjustment circuit 26 are connected to the output path from the CPU 20 to the oscillation circuit 10. However, the detection circuit 23 and the voltage adjustment circuit 26 can also be incorporated in the preamplifier unit 23.

The voltage adjustment circuit 26 includes a buffer, a voltage shift circuit, and the like. The power supply circuit 28 supplies power to the oscillation circuit 10 via the shield cable 4 in addition to the CPU 20.
The output circuit 27 is for outputting an object detection result to an external device, and outputs a binary signal indicating the presence or absence of the object. Hereinafter, this binary signal is referred to as an on / off signal, and the case where “there is an object” is referred to as “on state”. Further, when used for measuring the distance to an object, the output circuit 27 can output a voltage signal corresponding to the measured distance.

  The detection circuit 23 normally detects the signal extracted by the signal detection circuit 12, but depending on the configuration of the oscillation circuit 10, the detection circuit 23 may be connected to the resonance circuit 11 as shown by a one-dot chain line in the figure. is there.

  In the above, the oscillation amplitude of the oscillation circuit 10 decreases as the object approaches the head unit 1. The detection circuit 23 generates a detection signal indicating the magnitude of this oscillation amplitude. This detection signal is digitally converted by the A / D converter 24 and input to the CPU 20. This data input is performed at regular time intervals based on an output pulse from a timing generation circuit (not shown). The CPU 20 takes in the input data every hour as a measured value of the oscillation amplitude at that time, and this measured value. Are averaged every predetermined number of units. The averaged measurement value is compared with the threshold value in the memory to determine the presence / absence of an object, and the determination result is output from the output circuit 27. Further, the distance to the object can be obtained by collating the conversion table in the memory with the averaged measurement value.

  The CPU 20 generates an 8-bit digital signal representing the sensitivity adjustment value in response to a key operation on the operation unit 22. Hereinafter, this signal is referred to as a “sensitivity adjustment signal”. The sensitivity adjustment signal is updated each time the selection keys 224 and 225 are operated in the setting mode, and is output to the display unit 21 and the D / A converter 25. In addition, when a sensitivity adjustment value determination operation is performed, the CPU 20 stores the determination value in a memory. Further, in the actual measurement mode, the CPU 20 gives the sensitivity adjustment value read from the memory to the D / A converter 25 to control the operation of the oscillation circuit 10.

  The sensitivity adjustment signal analog-converted by the D / A converter 25 is given to the feedback circuit 13 of the oscillation circuit 10 via the voltage adjustment circuit 26. The feedback circuit 13 is designed such that the magnitude of the feedback current to the resonance circuit 11 varies depending on the voltage level of the sensitivity adjustment signal.

  FIG. 4 shows a specific example of the oscillation circuit 10 in the proximity sensor. 4 to 8, the portions corresponding to the resonance circuit 11, the signal detection circuit 12, and the feedback circuit 13 of FIG. 1 are surrounded by a dotted frame.

  The main part of the oscillation circuit 10 of FIG. 4 is the same as that disclosed in Patent Document 1 described above. Briefly describing the configuration, the base of an emitter follower transistor Q1 is connected to one end of a resonance circuit 11 including the coil L1 and the capacitor C1 through a series circuit of a resistor R1 and diodes D1 and D2.

  The emitter of the transistor Q1 is connected to a series circuit of resistors R2, R3, and R4, and the branch of the connection between the resistors R2 and R3 is connected to the base of the transistor Q2. A current mirror circuit including transistors Q3 and Q4 (PNP type) is connected to the collector of the transistor Q2. The emitter of the transistor Q3 is connected to the power supply Vcc via the resistor R6, and the collector is connected to the transistor Q2 similarly to the base. The emitter of the other transistor Q4 is connected to the voltage adjustment circuit 26 via a resistor R7, and the collector is connected to the feedback path of the resonance circuit 11.

  In this embodiment, a fixed resistor R8 is provided at a position corresponding to the sensitivity adjustment circuit 21 in FIG. 1 of Patent Document 1 and the sensitivity adjustment resistor Re in FIG. 16, that is, between the transistor Q2 and the ground potential. .

  In the above configuration, the signal of the resonance circuit 11 is input to the base of the transistor Q1 through the diodes D1 and D2, and then input to the base of the transistor Q2. Further, a signal change of the resonance circuit 11 is taken out by the signal detection circuit 12 including the transistor Q1 and resistors R2, R3, and R4, and is applied to the detection circuit 23.

  A current having the same magnitude as the current flowing through the transistor Q2 flows through the transistor Q3 of the current mirror circuit. On the other hand, the potential of the emitter of the transistor Q4 is equal to that of the emitter on the transistor Q3 side, but since the voltage adjustment circuit 26 is connected, the current flowing through the transistor Q4 due to the voltage difference between the output of the voltage adjustment circuit 26 and the emitter. The amount is controlled. That is, when the sensitivity adjustment signal from the D / A converter 25 increases, the voltage difference between the output of the voltage adjustment circuit 26 and the emitter of the transistor Q4 also increases, and the current flowing through the transistor Q4 also increases.

  FIG. 5 shows a second example of the oscillation circuit 10. The main part of this circuit is the same as that of FIG. 4, but the voltage adjusting circuit 26 and the D / A converter 25 are connected to the emitter of the transistor Q2 via a resistor R8. On the other hand, the emitter of the transistor Q4 is connected to the power supply Vcc similarly to the transistor Q3. In addition, about another structure, description is abbreviate | omitted by using the same code | symbol as FIG.

  In this second example, the collector current flowing through the transistor Q2 is controlled by the voltage across the resistor R8, that is, the voltage difference between the output of the voltage adjustment circuit 26 and the emitter of the transistor Q2. Therefore, when the sensitivity adjustment signal from the D / A converter 25 increases, the collector current of the transistor Q2 also increases, and the feedback current from the transistor Q4 also increases accordingly.

  FIG. 6 shows a third example of the oscillation circuit 10. The resonance circuit 11 of the oscillation circuit 10 is formed by connecting a series circuit of two capacitors C1 and C2 and a coil L1 in parallel. A PNP transistor Q11 is connected to the resonance circuit 11. A feedback circuit 13 is constituted by a current mirror circuit composed of the transistor Q11 and the second transistor Q12. Further, the resistor R11 interposed in the connection line between the connection between the capacitors C1 and C2 and the emitter of the transistor Q11 functions as the signal detection circuit 12. In this embodiment, the detection circuit 23 is directly connected to the resonance circuit 11.

  The emitter of the transistor Q12 is connected to a predetermined potential V1 lower than the power source Vcc, and the collector and base are connected to the ground potential via a resistor R13. The emitter of the transistor Q11 is connected to the voltage adjustment circuit 26 via the resistor R12.

  In the oscillation circuit 10, the signal extracted by the resistor R11 is input to the emitter of the transistor Q11, and a current corresponding to the signal change is fed back from the transistor Q11 to the resonance circuit 11. Here, the emitter potential of the transistor Q11 is the same as that of the transistor Q12, but since it is connected to the voltage adjustment circuit 26, the magnitude of the current changes due to the influence of the output voltage. That is, when the sensitivity adjustment signal from the D / A converter 25 increases, the voltage difference between the output of the voltage adjustment circuit 26 and the emitter of the transistor Q11 increases, and the feedback current also increases accordingly.

  FIG. 7 shows a fourth example of the oscillation circuit 10. The resonance circuit 11 in this example has the same configuration as that in FIG. 6, but the signal detection circuit 12 includes capacitors C3 and C4, an operational amplifier OP1, a pull-down resistor R21, and the like. The feedback circuit 13 includes transistors Q21 and Q22 (NPN type) constituting a current mirror circuit, resistors R22, R23, R24, R25, and R26.

  The operational amplifier OP1 inputs the signal of the resonance circuit 11 through the capacitor C3 and amplifies it by applying negative feedback. This amplified output is input to the detection circuit 23 via the capacitor C4, and further input to the bases of the transistors Q21 and 22 via the resistor R23. A resistor R25 is provided on the input line to the base.

  The collector of the transistor Q22 is connected to the power source Vcc via the resistor R24, and the emitter is grounded. The transistor Q21 has a collector connected to the power supply Vcc, an emitter-side connection path branched in two directions, and one of the transistors Q21 is connected to the voltage adjustment circuit 26 via a resistor R26. The other path is a feedback path to the resonance circuit 11 including the resistor R22.

  A current corresponding to the signal change of the resonance circuit 11 flows through the transistor Q21. This current is fed back from the emitter of the transistor Q21 to the resonance circuit 11 via the resistor R22. Here, when the sensitivity adjustment signal from the D / A converter 25 increases, the voltage difference between the output of the voltage adjustment circuit 26 and the emitter of the transistor Q21 increases, and as a result, the feedback current increases.

  FIG. 8 shows a fifth example of the oscillation circuit 10. In this example, a resonance circuit 11 similar to the example of FIGS. 4 and 5 is connected to a signal detection circuit 12 including an operational amplifier OP2. The feedback circuit 13 is provided with a current mirror circuit including NPN transistors Q31 and Q32.

  In addition to the operational amplifier OP2, the signal detection circuit 12 includes resistors R31 and R32 and a capacitor C5. The signal of the resonance circuit 11 is taken out by the resistors R31 and R32 and input to the operational amplifier OP2. The amplified output of the operational amplifier OP2 is output to the detection circuit 23 and the feedback circuit 13 via the capacitor C5.

  The bases of transistors Q31 and Q32 and the collector of transistor Q32 are connected to ground potential via resistor 35. The emitter of transistor Q32 is connected to negative potential Vee. The other transistor Q31 has a collector connected to the resonance circuit 11, a connection line on the emitter side is branched, one through a resistor R33 to the capacitor C5 of the signal detection circuit 12, and the other through a resistor R34. Are respectively connected to the voltage adjustment circuit 26.

  In this embodiment, a current flows from the resonance circuit 11 to the voltage adjustment circuit 26 via the transistor Q31. That is, when the oscillation amplitude becomes negative, current is drawn from the resonance circuit 11 by the transistor Q1, so that the oscillation amplitude increases to the negative side and energy is supplied to the resonance circuit 11. The feedback current in this case is determined by the voltage difference between the emitter of the transistor Q31 and the output of the voltage adjustment circuit 26.

  Of the five examples of the oscillation circuit 10, the oscillation circuit 10 having the configuration shown in FIGS. 4 and 5 has a point separated from the coil by a predetermined distance (assumed as point A) and a predetermined point behind it ( A large change occurs in the oscillation amplitude during the movement of the object between point A and point B), but it oscillates almost before the point A and saturates after the point B. To do. Such an oscillation state is called “hard oscillation”.

  On the other hand, in the oscillation circuit 10 having the configuration shown in FIGS. 6, 7, and 8, the oscillation amplitude changes gently according to the distance between the object and the coil until it reaches a certain level. Such an oscillation state is called “soft oscillation”. In any case of using the oscillation circuit of any configuration, the on / off signal can be turned on when the oscillation amplitude changes from a state larger than a predetermined threshold value to a state smaller than the threshold value. it can. Further, when it is necessary to measure the distance to the object, the soft oscillation type oscillation circuit 10 is used. In this case, a table of each characteristic curve shown in FIG. 9 (1) is incorporated in a memory, and the distance is determined by a method of matching the characteristic curve corresponding to the set sensitivity with the measured value of the oscillation amplitude. Can be sought.

  According to the oscillation circuit 10 shown in FIGS. 4 to 8, the feedback current to the resonance circuit 11 can be adjusted by changing the sensitivity adjustment signal from the D / A converter 25, thereby adjusting the oscillation amplitude. can do. Here, since the original sensitivity adjustment signal is an 8-bit digital signal indicating the sensitivity adjustment value, the voltage applied to the feedback circuit 13 is changed in a constant unit by changing the sensitivity adjustment value by one. be able to. Therefore, fine adjustment of sensitivity can be performed more easily than when sensitivity adjustment is performed by switching resistance.

  Next, FIG. 9A is a graph showing the relationship between the distance from the coil to the object and the oscillation amplitude, and shows that the relationship changes depending on the sensitivity adjustment value. The curve shown in this graph (hereinafter referred to as “characteristic curve”) is obtained when the soft oscillation type oscillation circuit 10 shown in FIGS. The distance on the horizontal axis is shown by normalizing the distance of the actual object with the rated detection distance (detection distance guaranteed by the manufacturer as being detectable) as 100%.

In this graph, a characteristic curve P ₀ indicates a relationship when the sensitivity adjustment value is 0, and a characteristic curve P ₂₅₅ indicates a relationship when the sensitivity adjustment value is 255 which is the maximum. Specialized curves corresponding to other sensitivity adjustment values are arranged in order from the smallest sensitivity adjustment value along the direction from the curve P ₀ to the curve P ₂₅₅ (the direction indicated by the arrow F in the figure).

  According to this graph, within the rated distance range, the oscillation amplitude increases as the sensitivity adjustment value increases. However, since the oscillation amplitude is saturated due to the influence of the internal voltage in the circuit, when the sensitivity adjustment value becomes large and the oscillation amplitude approaches the saturation state, the sensitivity is lowered.

  For example, in the graph of FIG. 9A, when measuring the distance to the object in the range from the point A to the point B on the distance axis, the change in oscillation amplitude with respect to the distance between A and B (the slope of the triangle for each curve) The measurement accuracy can be increased as the value increases. That is, the slope of each curve can be obtained as a parameter representing sensitivity.

  FIG. 9B is a graph in which the sensitivity value of each curve is associated with the oscillation amplitude at point A. As shown in this graph, until the oscillation amplitude reaches a certain value D, the sensitivity increases as the oscillation amplitude increases, but thereafter, the sensitivity decreases as the oscillation amplitude approaches the saturation state. Also, the characteristic curve corresponding to the sensitivity peak varies depending on the detection distance. Therefore, if a characteristic curve corresponding to the sensitivity peak is obtained for each detection distance, the object detection processing accuracy can be best achieved by setting a sensitivity adjustment value corresponding to the curve.

FIG. 10 shows a characteristic curve when the hard oscillation type oscillation circuit 10 shown in FIGS. In this figure also, the characteristic curve when the sensitivity adjustment value is 0 is P _0, and the characteristic curve when the sensitivity adjustment value is 255 is P ₂₅₅ . The characteristic curve based on other sensitivity adjustment values is located between P ₀ and P ₂₅₅ .

In the case of this type of oscillation circuit 10, the slope of the change in oscillation amplitude is the same in any curve, but the range in which the change occurs moves forward as the sensitivity adjustment value increases. Therefore, a characteristic curve P _x is obtained in advance so that the position (point C in the figure) where the user tries to detect an object is included in the range of change in oscillation amplitude, and a sensitivity adjustment value corresponding to the curve P _x is set. By doing so, the object can be detected stably.

  Further, as shown in FIG. 15 to be described later, the oscillation amplitude of the oscillation circuit 10 may change due to an external factor such as a temperature change. For this reason, when the oscillation circuit 10 having the characteristics as shown in FIG. 10 is used, if the distance from the coil to the point C is larger than the rated detection distance, the operation becomes unstable and the object cannot be detected correctly. There is sex. Therefore, the point C needs to be set ahead of the rated detection distance.

  In the case of using the hard oscillation type oscillation circuit 10 with the proximity sensor having the configuration shown in FIGS. 1 to 3, in consideration of the above points, the user is allowed to adjust the sensitivity by the operation shown in FIG. Yes. In FIG. 11 and the next FIG. 12, each step (STEP) is abbreviated as ST. In the following description, ST is used in accordance with this.

  This procedure is started after positioning the head portion 1 of the proximity sensor at a predetermined position. First, in the first ST1, an object to be detected is arranged at a position separated from the head unit 1 by a predetermined distance. In the next ST2, the sensitivity adjustment value is set to the initial value of zero in response to an operation such as selecting the sensitivity adjustment mode from the menu in the setting mode.

  Under this state, the sensitivity adjustment value is increased until the output from the sensor is turned on (state determined as “object present”) (ST3, 4). And when it will be in an ON state, the sensitivity adjustment value currently displayed on the display part 21 will be checked. If the numerical value displayed here is smaller than the predetermined lower limit value T1, ST5 becomes “NO”, and in ST7, a process of bringing the object closer to the head unit 1 is executed. If the displayed numerical value is larger than the predetermined upper limit value T2, ST6 is “NO”, and in ST8, the process of moving the object away from the head unit 1 is executed.

  After the process of moving the object closer to the head unit 1 or the process of moving the object away from the head unit 1, the process returns to ST2 to reset the sensitivity adjustment value by performing a resetting operation or the like. In the same manner as described above, the sensitivity adjustment value when the ON output is obtained is confirmed while gradually increasing the sensitivity adjustment value.

  When the sensitivity adjustment value at the time of ON output enters between the lower limit value T1 and the upper limit value T2 at a predetermined time, both ST5 and ST6 are “YES”, and the adjustment operation is finished.

  According to the above procedure, the user places an object at a desired distance from the head unit 1 and performs sensitivity adjustment until the on / off signal shifts from the off state to the on state. Here, if the sensitivity of the characteristic curve corresponding to the rated detection distance is set to the lower limit value T1, when the current position of the object is far from the rated detection distance, the output is turned on with a sensitivity adjustment value smaller than T1. In this state, it is necessary to move the object forward. Accordingly, it is possible to determine a detection distance that can stably detect an object, and at the same time, to perform sensitivity setting suitable for the detection distance. The upper limit value T2 may be set to a value according to the user's purpose, and the maximum 255 may be set as T2.

  Next, when the soft oscillation type oscillation circuit 10 is used for the purpose of measuring the distance to the object, generally, the maximum distance that the user wants to measure is set as the detection distance. It is desirable to adjust the sensitivity while maintaining it. Here, as shown in FIG. 9 (1), when the change of the oscillation amplitude near the set detection distance is small or the oscillation amplitude is close to the saturation state, the detection accuracy is unstable. Therefore, it is necessary to select a sensitivity adjustment value so that appropriate sensitivity (sensitivity in the vicinity of the peak in FIG. 9B) can be obtained for the detection distance.

  However, general users are not familiar with the oscillation characteristics as shown in FIG. In particular, when sensitivity adjustment is performed for the first time, there is a high possibility that the sensitivity adjustment value suitable for the detection distance is not grasped at all. Therefore, it is necessary to support the adjustment operation with an index instead of the sensitivity adjustment value.

  In consideration of the above problems, when the soft oscillation type oscillation circuit 10 is used in the proximity sensor having the configuration shown in FIGS. 1 to 3, the output value from the A / D converter 24, that is, the oscillation is displayed on the display unit 21. The amplitude value is displayed. Further, the procedure of the adjustment work is executed in a flow as shown in FIG.

  Also in the procedure of FIG. 12, the user initially sets the sensitivity adjustment value to 0 after placing an object at a position corresponding to the detection distance to be set (ST11, 12). Thereafter, the value of the sensitivity adjustment value is increased until the display of the oscillation amplitude reaches the predetermined value D (ST13, ST14). Note that the value of D needs to be larger than the threshold value for determining the presence / absence of an object and smaller than the oscillation amplitude in the saturated state. In addition, whatever the detection distance takes, if the oscillation amplitude at the position corresponding to the detection distance is set to D, the oscillation amplitude between the front and rear positions needs to show a sufficiently large change. is there. Considering such an oscillation state for each point and sensitivity adjustment value, it is desirable that D be a value around 70% of the oscillation amplitude under the saturation state.

  According to the above procedure, the user can set the sensitivity adjustment value so that the oscillation amplitude is suitable for detection. Therefore, the user can set a good sensitivity regardless of the detection distance set by the user. Can do.

  According to the procedures shown in FIGS. 11 and 12, the adjustment work can be performed while displaying an index for adjustment on the display unit 21. Therefore, even when a plurality of sensors having the same performance are used under the same conditions, after setting for one sensor according to the above procedure, the remaining sensors are set at the end of the first sensor adjustment. By performing adjustment so that the same value as the displayed value is displayed, it is possible to eliminate variations in sensitivity among sensors and perform highly accurate measurement. Even in the soft oscillation type proximity sensor, if the display is switched to the sensitivity adjustment value after the sensitivity setting is performed for the first sensor according to the procedure of FIG. 12, the sensitivity adjustment value is used as an index for the other sensors. The same setting can be made.

Next, the procedures shown in FIGS. 11 and 12 are both executed by the user. Instead, the CPU 20 adjusts the magnitude of the oscillation amplitude while updating the sensitivity adjustment value one by one. It may be. In this case, when the hard oscillation type oscillation circuit 10 is used, the sensitivity adjustment value may be updated until the oscillation amplitude reaches the object detection threshold value. When the soft oscillation type oscillation circuit 10 is used, the sensitivity adjustment value may be updated until the oscillation amplitude reaches the value D.
For the hard oscillation type oscillation circuit 10, an error code is displayed on the display unit 21 when the sensitivity adjustment value when the oscillation amplitude reaches the threshold value becomes smaller than the lower limit value T1. , It is desirable to tell the user to that effect.

  Next, according to the configuration shown in FIG. 1, the preamplifier unit 23 constitutes a detection unit together with the head unit 1, so it is necessary to manufacture each head unit 1, but the amplifier unit 2 includes a plurality of heads. A configuration common to the unit 1 can be adopted. In this case, the amplifier unit 2 can set an optimum sensitivity according to the characteristics of each head unit 1.

  FIG. 13A illustrates three head portions 1 (in this figure, heads A, B, and C are shown for convenience) having different relationships between oscillation amplitude and distance. FIG. 13 (2) shows the result of adjusting the characteristic curve of FIG. 13 (1) by the conventional method of changing the resistance value, and FIG. 13 (3) shows the result of this embodiment for each characteristic curve. The results of adjustment using the sensitivity adjustment value are shown respectively.

  When performing adjustment by switching a variable resistor for sensitivity adjustment, it is difficult for the user to grasp an appropriate operation amount of the volume. As a result, as shown in FIG. 13 (2), the change in the oscillation amplitude after the adjustment varies depending on the head unit 1, and there is a problem that the set sensitivity varies greatly.

  On the other hand, in the proximity sensor of this embodiment, as described above, the sensitivity adjustment value can be adjusted while displaying the numerical value indicating the oscillation amplitude. Therefore, as shown in FIG. 13 (3), by adjusting the sensitivity adjustment value for each head so that the difference in oscillation amplitude of each head becomes small, the variation in sensitivity between the heads can be reduced. it can.

  Further, according to the proximity sensor having the configuration shown in FIG. 3, since the value of the feedback current can be determined by the CPU 20, more detailed control can be performed according to the installation environment and purpose of use of the sensor.

  FIG. 14 shows a configuration in which the oscillation amplitude can be controlled according to the temperature change around the sensor. Since the main configuration of this figure is the same as that shown in FIG. 3, the same reference numerals as those in FIG.

  In the embodiment of FIG. 14, temperature sensors 61 and 62 are provided in the head unit 1 (not shown here) and the amplifier unit 2, respectively, and measured values by the temperature sensors 61 and 62 are stored in the amplifier unit 2 in the CPU 20. An input unit 29 for inputting is provided. The memory attached to the CPU 20 incorporates a correction table for correcting the sensitivity adjustment value based on the temperature in advance. In this correction table, the temperature values are classified into a plurality of sections, and the correction values of the sensitivity adjustment values are associated with the sections.

  Further, the temperature sensor may be provided in one of the head unit 1 and the amplifier unit 2. In particular, when the head unit 1 is placed in a place where the temperature change is large, it is desirable to install a temperature sensor on the head unit 1 side.

FIG. 15 shows the principle of correction based on temperature information based on the relationship between the distance and the oscillation amplitude when the ambient temperature is 25 degrees, 60 degrees, and −10 degrees.
FIG. 15 (1) is a characteristic curve before correction for each temperature. According to this, when the ambient temperature increases, the oscillation amplitude increases, and when the ambient temperature decreases, the oscillation amplitude decreases.
FIG. 15B shows an example in which the characteristic curve at 60 degrees and the characteristic curve at −10 degrees are corrected so as to match the characteristic curves at 25 degrees, respectively.

  Based on the above principle, the CPU 20 corrects the sensitivity adjustment value input from the operation unit 22 based on the temperature measurement value, and outputs the corrected value as a sensitivity adjustment signal. The correction value necessary for this correction is read from the correction table in the memory.

  For example, a predetermined temperature (for example, 25 degrees) is set as a room temperature in advance, and when the temperature detected by the temperature sensors 61 and 62 is higher than the room temperature, the sensitivity adjustment value is corrected to a value smaller than the input value. Reduce the oscillation amplitude. When the temperature detected by the temperature sensors 61 and 62 is lower than the normal temperature, the oscillation adjustment is increased by correcting the sensitivity adjustment value to a value larger than the input value.

FIG. 16 shows an example in which the sensitivity adjustment signal is used for control when a plurality of proximity sensors are used in the vicinity.
In the case where a plurality of proximity sensors are arranged close to each other, conventionally, in order to prevent mutual interference between the sensors, control is performed to alternately switch the sensors to oscillate. FIG. 16 (1) is a specific example of this control, and the three sensors A, B, and C are oscillated in order for the same length period. Note that the oscillation switching of each sensor can be controlled by a control signal from an external host device or by mutual communication between sensors.

According to the above control, any sensor can perform object detection processing without being affected by the operation of other sensors.
However, in the conventional control, as shown in FIG. 16 (2), since a sufficiently large signal is not output at the rising edge of the oscillation, the time T until the oscillation becomes stable becomes longer, and noise is generated during that time. There was a risk of being affected.

  On the other hand, in the proximity sensor having the configuration shown in FIG. 3, as shown in FIG. 16 (3), the sensitivity adjustment signal at the rise of oscillation is made larger than the original set value, and then the sensitivity adjustment signal is changed to the original value. It is possible to execute control that returns the value. As a result, the time T until the oscillation is stabilized can be significantly shortened compared to the conventional case, and stable detection can be performed.

  Next, the proximity sensor of the type that detects the oscillation amplitude has been described above as an example, but the present invention can also be applied to a frequency detection type proximity sensor. FIG. 17 shows an application example thereof.

  In the proximity sensor of this embodiment, the configuration of the oscillation circuit 10 is the same as that in FIG. 3, but the amplifier unit 2 is provided with a frequency counter 201 in place of the detection circuit 23 and the A / D converter 24. In this embodiment, by increasing or decreasing the sensitivity adjustment signal from the D / A converter 25, the amount of feedback of current can be increased or decreased, and the oscillation frequency can be adjusted.

  Also in this embodiment, the sensitivity according to the input value can be set by inputting the sensitivity adjustment value through the operation unit 22. Also in this embodiment, it is possible to set a sensitivity suitable for object detection by adjusting the sensitivity adjustment value until the display of the frequency counter 201 shows a predetermined value.

  FIG. 18 shows another example of an amplitude detection type proximity sensor. Although the main configuration of the proximity sensor of this embodiment is the same as that shown in FIG. 3, the relationship between each configuration and the power supply circuit 28 is shown in detail.

  In the proximity sensor of this embodiment, a volume including a variable resistor Re is provided as the operation unit 22 instead of the configuration of FIG. The variable resistor Re has one end connected to the ground potential and the other end connected to the positive potential V via the resistor R41. The A / D converter 202 is connected to a connection line between the variable resistor Re and the resistor R41. The A / D converter 202 is connected to the CPU 20 in the same manner as the A / D converter 24 on the detection circuit 23 side.

  The A / D converter 202 detects a potential between the variable resistor Re and the resistor R41. The CPU 20 takes in this detected potential as the operation amount of the volume, converts it into a predetermined numerical value, and displays it on the display unit 21. At the same time, the CPU 20 outputs the numerical value output to the display unit 21 to the D / A converter 25 as a sensitivity adjustment signal.

  According to this configuration, the amount of rotation of the volume can be expressed numerically and clearly shown to the user, so that variations in settings can be eliminated. Further, the feedback current can be adjusted for each fixed unit by a digital amount of sensitivity adjustment signal.

Next, FIG. 19 is a modification of the configuration of FIG. 18, and the same reference numerals as in FIG. 18 are given to the common configurations. In the proximity sensor of this embodiment, the circuit connected to the detection circuit 23 is replaced from the A / D converter 24 to the signal processing circuit 203, and the signal processing circuit 203 is directly connected to the output circuit 27. The signal processing circuit 203 includes a comparator and the like, compares the detected signal with a predetermined threshold value, and outputs an on / off signal indicating the comparison result to the output circuit 27.
According to this configuration, since the presence / absence determination of the object can be performed without using the CPU 20, the response of the sensor can be accelerated.

  In each of the above embodiments, the feedback current is adjusted by adjusting the voltage applied to the feedback circuit 13 of the oscillation circuit 10, but instead of this, a circuit for performing current control, The feedback current of the oscillation circuit 10 may be adjusted using an IC or the like. Also in this case, the amount of current can be controlled according to the value of the sensitivity adjustment signal from the CPU 20.

It is a perspective view which shows the external appearance of the proximity sensor to which this invention was applied. 3 is a top view illustrating a detailed configuration of a display unit and an operation unit of an amplifier unit 2. FIG. It is a block diagram which shows the electric constitution of a proximity sensor. It is a circuit diagram which shows the structural example of an oscillation circuit. It is a circuit diagram which shows the structural example of an oscillation circuit. It is a circuit diagram which shows the structural example of an oscillation circuit. It is a circuit diagram which shows the structural example of an oscillation circuit. It is a circuit diagram which shows the structural example of an oscillation circuit. It is a graph which shows the relationship between the characteristic curve of oscillation amplitude and distance, and sensitivity. It is a graph which shows the other example of the characteristic curve of an oscillation amplitude and distance. It is a flowchart which shows the procedure of adjustment work. It is a flowchart which shows the procedure of adjustment work. It is a graph which shows the example of the sensitivity adjustment with respect to multiple types of head parts. It is a block diagram which shows the other example of the electric constitution of a proximity sensor. It is a graph which shows the example of the sensitivity adjustment according to a temperature change. It is explanatory drawing which shows the example of control in the case of performing intermittent operation | movement. It is a block diagram which shows the other example of the electric constitution of a proximity sensor. It is a block diagram which shows the other example of the electric constitution of a proximity sensor. It is a block diagram which shows the other example of the electric constitution of a proximity sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Head part 2 Amplifier part 10 Oscillation circuit 11 Resonance circuit 12 Signal detection circuit 13 Feedback circuit 20 CPU
21 Display unit 22 Operation unit 25 D / A converter 27 Output circuit 27

Claims (7)

An oscillation circuit including a coil; a detection unit that detects a metal object using an oscillation amplitude of the oscillation circuit; an output unit that outputs a detection result of the detection unit; and an oscillation in response to a change in the distance between the coil and the metal object. In a proximity sensor comprising an adjusting means for adjusting the state of change in amplitude,
The oscillation circuit incorporates a feedback circuit designed so that the amount of feedback current varies depending on the applied voltage, and the adjusting means includes a voltage level applied to the feedback circuit in the oscillation circuit. A proximity sensor comprising: a signal generating means for generating an adjustment signal represented by a digital quantity; and a signal output means for converting the adjustment signal into an analog signal and outputting the analog signal to the feedback circuit. The proximity sensor according to claim 1,
An operation unit for sensitivity adjustment and a display unit for displaying information indicating the value of the adjustment signal or information indicating the magnitude of the oscillation amplitude are provided,
The signal generation means of the adjustment means sets the value of the adjustment signal according to the operation of the operation unit,
Display control means for controlling the display of the display section using the value of the adjustment signal set by the signal generation means or the oscillation amplitude when the signal after analog conversion of the adjustment signal is output to the feedback circuit Proximity sensor comprising. The proximity sensor according to claim 1,
The adjustment means includes a control means for causing the signal generation means to repeatedly execute a process of stepwise changing the value of the adjustment signal in a constant unit until the oscillation amplitude reaches a predetermined value; and the oscillation amplitude A proximity sensor comprising: registration means for registering the value of the adjustment signal when becomes a predetermined value. The proximity sensor according to any one of claims 1 to 3,
A temperature measuring means for measuring the ambient temperature is provided,
The proximity sensor, wherein the signal generating means of the adjusting means includes a correcting means for correcting the value of the adjusting signal based on the measured value by the temperature measuring means. An oscillation circuit including a coil; a detection unit that detects a metal object using an oscillation amplitude of the oscillation circuit; an output unit that outputs a detection result of the detection unit; In a proximity sensor comprising an adjusting means for adjusting the state of change in amplitude,
The oscillation circuit incorporates a feedback circuit designed to change the amount of feedback current depending on the applied voltage, an operation unit for setting a voltage value to be applied to the feedback circuit, and And a display unit for displaying information indicating the set value or information indicating the oscillation amplitude,
The proximity sensor is configured to apply a voltage that changes according to the setting of the operation unit to a feedback circuit in the oscillation circuit. The proximity sensor according to claim 5,
The proximity sensor is a numerical sensor that is a numerical value display unit that displays a numerical value corresponding to a voltage set by the operation unit or a transmission amplitude of an oscillation circuit to which the voltage is applied. The proximity sensor according to any one of claims 1 to 6,
In the adjusting means, the voltage applied to the feedback circuit is changed from a voltage for setting an oscillation amplitude having a magnitude that does not react to the metal object in response to an external signal to a voltage that is normally set. A proximity sensor that includes a voltage control unit that adjusts the applied voltage so that the voltage to be normally set after a lapse of a predetermined time from the change.

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